The present invention relates to a power source device for ion sources including a directly heated filamentary cathode.
In an ion source of a type which has a directly heated filamentary cathode and which causes arc discharge to produce a plasma, an arc discharge current flows into the main portion of the filamentary cathode and then to a negative voltage terminal thereof. Since the arc discharge current is superposed on a heating current for heating the filamentary cathode, local overheating occurs at the vicinity of the negative voltage terminal of the cathode. The filamentary cathode then locally evaporates, resulting in a short service life of the cathode.